A tyrosine hydroxylase assay in microwells using coupled nonenzymatic decarboxylation of Dopa

A radiometric assay for tyrosine hydroxylase employing a coupled nonenzymatic decarboxylation of l-[¹⁴C]Dopa formed from l-[¹⁴C]tyrosine has been adapted for performance in a 96 microwell culture plate. The method uses an easily manufactured plate holder to compress blotting paper impregnated with methylbenzethonium hydroxide against the top rim of each well. This forms isolated, airtight compartments in which ¹⁴CO₂ is evolved and quantitatively absorbed into the blotting paper. The method is sensitive enough to detect the production of less than 5 pmol of ¹⁴CO₂. A major advantage of this system is that cells can be grown in tissue culture and subsequently assayed for tyrosine hydroxylase activity in the same well. The method is more facile than previously devised procedures, allowing for the simultaneous assay of up to 96 samples totally contained in a single, compact, portable unit.